• carbon cycling;
  • carbon isotope;
  • fine-root turnover time;
  • Monte Carlo simulations;
  • numerical model;
  • radiocarbon;
  • root model parameterization;
  • roots


  • • 
    We used an inadvertent whole-ecosystem 14C label at a temperate forest in Oak Ridge, Tennessee, USA to develop a model (Radix1.0) of fine-root dynamics. Radix simulates two live-root pools, two dead-root pools, non-normally distributed root mortality turnover times, a stored carbon (C) pool, and seasonal growth and respiration patterns.
  • • 
    We applied Radix to analyze measurements from two root size classes (< 0.5 and 0.5–2.0 mm diameter) and three soil-depth increments (O horizon, 0–15 cm and 30–60 cm).
  • • 
    Predicted live-root turnover times were < 1 yr and ∼10 yr for short- and long-lived pools, respectively. Dead-root pools had decomposition turnover times of ∼2 yr and ∼10 yr. Realistic characterization of C flows through fine roots requires a model with two live fine-root populations, two dead fine-root pools, and root respiration. These are the first fine-root turnover time estimates that take into account respiration, storage, seasonal growth patterns, and non-normal turnover time distributions.
  • • 
    The presence of a root population with decadal turnover times implies a lower amount of belowground net primary production used to grow fine-root tissue than is currently predicted by models with a single annual turnover pool.